the difference between "anyone" and "whoever"

[chance22]

Here the sentence: I hope ____(whoever/anyone) that was involved in that accident was all right.
I know "whoever" is to be used here, but I'm not clear why "anyone" is not acceptable in the sentence. Is it because "anyone" is directed to a group of known people, whereas "whoever" is used more for an unknow group of people? Or is it because "anyone" can't be followed by a subordinate clause?

 

[Raymott]

Who told you that 'whoever' should be used here? "I hope whoever that was involved..." is wrong. It would be correct without 'that'.
If I had that choice, I'd go with 'anyone', even though it's still not ideal. It's not a good choice of alternatives.

 

[Matthew Wai]

'I hope anyone involved in that accident was all right.'
'That was' is omitted, is it OK?

 

[Raymott]

Yes.

 

[chance22]

Who told you that 'whoever' should be used here? "I hope whoever that was involved..." is wrong. It would be correct without 'that'.
If I had that choice, I'd go with 'anyone', even though it's still not ideal. It's not a good choice of alternatives.

It's from an workbook on grammar. I guess the sentence as well as the key is not correctly provided, which makes me confused. Now it's clear. Thank you for the explanation