Php is single-threaded Synchronize blocking, how does multithreading of curl batch run?

php is a single-threaded Synchronize blocking, while curl_multi can implement multithreading. Aren"t the two contradictory?
ask the boss to explain, thank you!

Php
Aug.11,2021

the underlying layer is implemented through select IO multiplexing.

single-thread initiating network IO, can push multiple requests to the IO collection, and when an IO event occurs, the response value is read. Here, it is handled by a single thread, and if multiple requests are readable, they can only be processed one by one.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b4049a-4db9c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b4049a-4db9c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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