True I hadn't considered that but then neither do they. Instead they deem it unlikely because the biology was impossible. Something they really shouldn't dismiss consider parahumans.
Honestly your answer is probably correct I was just annoyed they were focusing on something that while making sense to us doesn't in-universe with there more limited context on parahuman's origins.
Interworld portal technology, as far as the vast majority of people know, is extremely rare and very controlled. So it's not unreasonable to think that this possibility is quite low probability, especially since the insect they're gaping at
is a completely recognizable earth life form according to expert opinion. It's much, much too large to exist according to current scientific understanding, which almost inevitably suggests to them that Parahuman powers are involved.
When in doubt, A Parahuman Did It.
And, don't forget, they're the
Parahuman Response Team. They have a very obvious institutional bias to reaching for a Parahuman explanation whenever they run into something they haven't seen before, and in all honesty that's usually the answer. In this case it
is the answer, of course, but not quite in the way they're thinking...
It would require some sort of power-based action to have an insect that big, basically. It would require a completely different power-based action to bring something like that to their world and
still require a power-based action to allow it to survive, unless it's running on completely different principles (It is but they don't have any way to know that at the moment.) The simpler explanation is to go with the option that only one power-based action is involved, rather than two.
Note they didn't reject it out of hand, they just moved it to the lowest probability end of the list of possible reasons. There are more likely causes based on prior experience...
Also I had to stop writing that scene eventually and couldn't really justify an exhaustive list of every single possible idea they might have had. That meeting went on
forever!