The words sewed, sowed sound the same but have different meanings and spellings. Why do sewed, sowed sound the same even though they are completely different words?
The answer is simple: sewed, sowed are homophones of the English language.
Simple past tense and past participle of sew.
Simple past tense and past participle of sow.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.