He's wrong and you/Wikipedia are right, BTW. Halons were banned in 1994, before datacenters became commonplace. Argon and other inert gas fire suppression systems (of which Halon is one, but a banned one) are used instead.
The article is talking about 1971, long before Halon was banned. It was commonplace to find Halon installations in computer rooms in the 1980s.
The 90s called and would like a word with you.
The op's a bit outdated, but not completely wrong. Even now a lot of data centers use various halon replacements rather than Argonite, though there are a number of different gaseous fire suppressants used in data centers these days.
The gaseous system was one-shot. If the fire continues or restarted, or another fire occurred before the system was recharged, water sprinklers would save the building.
Redundant systems. Of course, some data centres probably have redundant gaseous suppression too.