Interference and obstruction are calls that always require umpire judgment. They are usually "had to be there" plays and sometimes it's hard to make that sort of judgment without actually seeing the play. The right call can hinge on the fine details of what exactly each player was doing, when they did it and how they did it.
NCAA rules are somewhat more lenient than lower amateur levels when it comes to contact between players. One rule that is identical, however, is the the "crash rule" for interference. This rule states that if the fielder is already holding the ball and waiting to make a tag, the runner may not deliberately, with great force, remain on her feet and crash into the fielder. if she does, then it is interference. If the act is judged to be flagrant or malicious, then the runner is also ejected.
But that rule would not apply here since, by the description, the catcher had not yet gained control of the ball and was not stationary, waiting to make a tag. So, we can take crash interference off the table, which is the rule most people want called whenever there is a collision at the plate.
I'd also have to ask if the catcher was moving in any way when the ball arrived. When a defensive player suddenly or unavoidably moves into the path of a runner, that can cause a crash that isn't the runner's fault, so the runner wouldn't be penalized. Was the catcher maybe moving to block the plate as the ball arrived? Under NCAA rules, a fielder can legally block the base without the ball if they are in the act of receiving a throw. Any subsequent collision could be ruled as "incidental", neither obstruction or interference.
Unfortunately, while I am familiar with college rules, I don't really know the nuances of how they instruct their umpires to interpret these plays. Here are a couple of pasages from their rule book:
The rules committee is concerned about unnecessary and violent collisions with
the catcher at home plate and with infielders at all bases. The intent of this rule
is to encourage base runners and defensive players to avoid such collisions,
whenever possible.
12.14.1 A defensive player shall not block the base, plate or baseline without
possession of the ball or not in the immediate act of catching the ball.
EFFECT: Delayed dead ball is signaled. Obstruction is called and the base
runner is declared safe. Each base runner must return to the last
base legally touched at the time of the infraction. Exception: If
the base runner collides flagrantly, the ball is dead, and although
the base runner is declared safe on the obstruction call, the
player is ejected.
Apparently, whatever the runner did was not judged to be flagrant by the umpire. If it had been, the runner would have been ejected, but her run still would have counted.
Simply because there is contact between the defensive and offensive
player does not mean that obstruction or interference has occurred.
Note: If both the fielder and base runner are within their legal rights, neither
player shall be penalized for the incidental contact.
Right or wrong, it seems like maybe the umpire based his ruling on this rule and judged the contact to be incidental. This is what I meant earlier by the college rules being somewhat more lenient when dealing with collisions. There is more of a "let them play" attitude than in ASA or high school ball.
So...was this interference or not? One person's judgment might be different than another's, and the legality of the play might depend on the fine details we didn't see. All I can say for sure is that in the opinion of the umpire who actually observed the play on the field, it must not have been interference!
