I think you were right in raising a flag on that comment, but you should have went with "rude or offensive" instead of "not constructive". I think a rude or offensive comment is worse for the site than a non-constructive comment. So if you took offense, I think it would be more appropriate to use that flag instead. Being rude is never constructive, so "rude or offensive" is actually more specific than "not constructive". I mean, assuming that you took offense.

On a side note... I don't mean to start an argument about who started it, but your own comment probably also came off as rude. I mean, [lmgtfy](http://lmgtfy.com/?q=prosperity+mtg) on a [new user](http://meta.stackexchange.com/questions/172970/negative-comments-drive-new-users-away-how-can-we-fix-this/173050#173050) seems [really inappropriate][1].

  [1]: http://meta.stackexchange.com/questions/15650/ban-lmgtfy-let-me-google-that-for-you-links