Is this a warning sign? If so, what does this indicate?

There’s this man I met online on here, who calls himself *Bob* (not his real name). Bob has commented that I haven’t been online much, when I have been online fairly often. I offered Bob my number, to use WhatsApp. Bob declined giving me his number. He said that he hates WhatsApp and doesn’t use it anymore, but gave me his email address and suggested we talk through my gmail account. What is this indicative of? I did have a guy pursuing me, following me around and tracking me online, even on here, who recently responded to my general questions on here, for the public. I also know that this is the sort of thing that married men do to cover their tracks. My mum said it’s likely to be someone who wants to hack into my gmail account to get my personal details. A con artist. Which is most likely?

Updates
4 mo
I’m autistic and quite naive and gullible, so all I know is that something doesn’t add up. But I don’t really know why.
Is this a warning sign? If so, what does this indicate?
Post Opinion