The old alum returned to his school — the children didn't know him, and smilingly asked where the visitor had come from.
Tips
history
From 《回乡偶书·其一》 by 贺知章 (He Zhizhang, Tang dynasty): '少小离家老大回,乡音无改鬓毛衰。儿童相见不相识,笑问客从何处来.' He Zhizhang wrote it after retiring to his hometown at age 86 after a 50+ year absence. Canonical Chinese textbook poem about homecoming.
usage
相 here is the grammatical marker 'toward one another / a target' (same as in 相信, 相爱), not 'appearance.'