Sharepoint - Strange encoding when my site column name start with a number

When you create a column name beginning with numbers in UI , SharePoint converts it internally as below:

_x0032_ + Rest of the field name beginning with second digit.

To answer your questions

1) Avoid column names beginning with numbers as general thumb rule/practice. If you must, then use Powershell to set internal name/display name.

2) Powershell/SSOM/CSOM works differently compared to UI as you have access to schema XML. Hence, you dont face this issue of weird internal column name. As mentioned above, as a practice dont use numbers as starting characters in the column name.

3) It's fine if other characters are numbers.