I believe it’s correct. If you sort say “A”, “AA”, “AAA” then you get

1. A
2. AA
3. AAA

Because the first character is compared, which are all the same, then the second. The first one has no second character, so it comes first. The second has no third character, so it comes before the third item.

In your scenario, you have:

1. 5
2. 5.5

The first characters are the same, so it looks at the second character. Item 1 has no second character so it comes first.

Scenario 2:

1. 5.5 A
2. 5 A

The first character is the same, so it looks at the second character. The second characters are “.” and " ". The “.” comes first in the character ranking so is shown first.