I want to ask that, if a website can detect multiple tabs/browsers are opening, can it also detects Tor?
Yes any websites can see that you are using Tor. They see that because you are visiting their website via a Tor exit node. They don't know who you are unless you tell them, but they see "someone" is visiting using Tor.
Can another program running on your computer see that you are using Tor? Yes, there are no attempts to hide that.