The wallet itself is safe (for all I know, there is no absolute security). He got trojan'ed or something, lost his private keys one way or another..

I can't vouch for https://www.triangles.network because it's a community-built site and I don't control the domain or the files hosted there. I do assume those files are fine tho.

If you want to be 100% sure, download your version of the TRI wallet from https://triangles.technology/. Yes, I know the SSL-cert is expired, I'll try to find the time and fix it sometimes this weekend (the expired cert poses no security risk of any kind).