"Commercial activity" can be as benign as "There are membership fees", "There's a soda machine in the corner that takes coins", "I'm doing it to brush up my CV" (increasing future income potential), or "There are ads on the website".
As such, any of these might trigger the "only for ... non-commercial ... use" clause. So folks generally just don't sweat it.
The Sustainable Use License doesn't seem to contain a blanket ban on commercial use. Here's what it says on limitations:
"You may use or modify the software only for your own internal business purposes or for non-commercial or personal use. You may distribute the software or provide it to others only if you do so free of charge for non-commercial purposes. You may not alter, remove, or obscure any licensing, copyright, or other notices of the licensor in the software. Any use of the licensor’s trademarks is subject to applicable law."
Studying the software in a commercial setting seems to be permitted.
As such, any of these might trigger the "only for ... non-commercial ... use" clause. So folks generally just don't sweat it.