You won’t get bed bugs from lying down on grass, Some other kind of biting insect perhaps but bed bugs are very specialised pests. Are you sure they were bed bugs?
@flutherother No I’m not sure. They were bugs in my bed. Landlord said that they were bed bugs. The residents kept a stray cat in my bed room while I was gone. left purple and red bite marks in my body.
The bugs in your bed may have been bed bugs. They were probably left by a previous tenant. They are horrible things and hard to get rid of. They can transfer from apartment to apartment in your luggage.
Chances are low but not impossible. More possible way is you went to some place which was infested with bugs or met someone who had bugs on his body / clothes. They hide at places where you can’t see them easily and they are so tiny. On grass it is possible only if someone having bed bugs on his body was there before you sat on the grass.