That sort of thing does happen with mangos. Not real common, but not unusual.

Thanks. Is it safe to eat?

I doubt that any odd deformity like this on would be unsafe to eat. Once you open it you will probably see that it's just a skin deformity.

You may want to plant that seed, you never know... it could make a whole new cultivar of unusual mango.

Yes, mangos that you hang off a rail, LOL.

Maybe its happy to see you

It's a Cashew-nut-mango. Mango and Cashew nut share the same origin I believe, and one of the cashew remnant gene rears its head on your mango. This little thing will turn yellow and become the nut.