If the site is compromised it doesn't matter if you use it offline or online. The owner of the site could easily set it up to generate compromised private keys. Other users have complained about this site too. It is not safe.
Do you know how much people have complained about electrum already ? Countless..
Do you regard electrum as not being safe too ?
I do not agree with any kind of paper wallet creation through websites (regardless whether online or offline). But without proper evidence, or at least some indications, calling a random paper wallet website not safe is not completely correct.
No website is safe for newbies. No web wallet is. And no desktop wallet is.
Nothing is safe for a user without common sense. Not even a hardware wallet.
Are there any indications why this website should be avoided (besides newbies complaining about it) ?
of it years ago. He may have sold it to a scammer or he may have broken bad himself. It cannot be trusted.