I agree with most of the above replies. First, if you're not somehow involved in their lab, how do you know the details of the type of data they collect, how everything is coded, and what everything means? Secondly, in my opinion, yes it is very weird to email a PI that you have no connections to and ask for their data. Even between PI's working together, people are generally very protective of their data and need special permission for undergrads to even handle the data, not to mention analyze.
The best thing may be to bring it up to your current PI and maybe she/he can ask the other PI if you can use their data. This has happened multiple times in my lab, and it has always worked out for the student. If you are interning at multiple labs, then that's a different story.