PowerShell will always evaluate using the type of the left-side argument. Since you have a boolean on the left PowerShell will try and cast "Hello" as a boolean for the purpose of evaluating with -eq.
So in your case "hello" is converted to a boolean value [bool]"hello" which would evaluate to True since it is not a zero length string. You would see similar behavior if you did the opposite.
PS C:\> "hello" -eq $true
False
PS C:\> [bool]"hello" -eq $true
True
In the first case $true is converted to a string "true" which does not equal "hello" hence false. In the second case we cast "hello" to boolean so the -eq will compare boolean values. For reasons mentioned about this evaluates to True.
Another good explanation comes from this answer which might get your question flagged as a duplicate: Why is $false -eq "" true?
