without having to download anything, I still get an excess of ram from that website, and a moderate CPU consumption that makes the fans sound like I'm playing a heavy video game. But this weird behavior only happens sometimes, the first thing I think of is illegal cryptocurrency mining but I'm not sure about that.
I asked the website administrator and he didn't give any answer as it is a legitimate website it seems unlikely to be malicious unless it has been hacked and they don't know about it.