Federal Aviation Regulations - Part 101, Subpart E, 101.41 (b)
This subpart prescribes rules governing the operation of a model aircraft (or an aircraft being developed as a model aircraft) that meets all of the following conditions as set forth in section 336 of Public Law 112-95:
(a) The aircraft is flown strictly for hobby or recreational use;
(b) The aircraft is operated in accordance with a community-based set of safety guidelines and within the programming of a nationwide community-based organization;
AMA National Model Aircraft Safety Code Section B, Number 7
"Under no circumstances may a pilot or other person touch an outdoor model aircraft in flight while it is still under power, except to divert it from striking an individual."
If you have a nationwide community-based organization other than the AMA, please post their rules so we will all have a choice.
The logic of your argument is certainly sound and so technically, yes, it would appear that hand catching would go against that guideline. Since there is no other current, credible CBO, it could therefore invalidate any claim to be flying under Part 101, but I still doubt that the FAA would have any interest in making that argument.
Are you posing this as a purely hypothetical issue, or do you see it as a tangible risk to hobbyists?