@Rikki ******
Not in all cases no.. Entirely DTA dependant.
'Some' pensions are taxed at source, eg us social security or military pensions, but most tax deferred pensions, private pensions, etc etc Even some government operated ones like Oz super are fully taxable in Thailand (on remittance, over 180 days, all the many variables). ISA SIPP etc pensions are tax delaying systems and are taxable where resident at disbursement.
Also these days people talk about pensions and often include shares, dividends, other investments they make for old age as 'pension' or mistakenly believe them to be 'savings' as Thailand defines it. Those are all 'income' also potentially capital gains if remitted..
The law here is incredibly broad, the enforcement is non existent. Thailand 101.