To answer your question. Yes I think the EPA is pretty dumb.
Fair, but if you think the only way they have to access your information on this forum is to entrap you into making a post..... well.... you would not be right.
The odds of this guy being a new legitimate member looking for help is many times higher then the odds of him being a deep cover EPA agent looking trying to connect forum names to vin number or something.
Googles spiders are constantly indexing this forum, as well as every other site online to keep there search engine results up to date.
This forum is run on a database of some sort, assuming that the people running this site are not completely, and totally incompetent, that database is regularly backed up for disaster recovery or roll backs ect.
I guarantee you neither would hesitate to comply with a legal request for those records.... not that that would be needed, since the entire contents of this site since it launched is publicly available via search engines....
Once you put something on the internet, no matter what it is, or how fast you delete it, it will be there forever if you know where to look.