“Learnt” and “learned” are two acceptable forms of the past simple/past participle of the verb learn, which means exactly the same thing. Learn is an irregular verb in the British English where the past tense is spelt with a ‘t’ at the end – [learn/ learnt]. Conversely, Learn is a regular verb in the American English where the past tense is spelt with a ‘ed’ at the end – [learn / learned]. Thus, neither is incorrect as “learnt” is more commonly used in the British English, and “learned” in American English.
There’re other forms of verbs of the past simple/past participle in both American and British English. Some of these are: burned/burnt, smelled/smelt, spelled/spelt, spilled/spilt, spoiled/spoilt, dreamt/dreamed, leant/leaned, smelt/smelled etc.