Many of the telegram groups which give signals are run by the same people, I have noticed on multiple occasions of the groups giving the same signals. Many of the groups also conduct coordinated pump and dumps, and they usually send it in all the groups to gather a greater audience. Although some of the signals turn out to be correct, always do your own research before making a trade.
Indeed, it is better to avoid joining these groups or at least not take their word and their speculations seriously, because as you said theier predictions are based on nothing but mere guesses or hopes, and they say them just to influence people's decisions so it could meet thier intrest , and also they only give speculation about coins they are interested in and want to pump and dump.