I'm sure the wording "was first" tripped up a few people.
A quick google search on 802.11a will show you that it was only deployed on 5 Ghz
"The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band, and uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM) with a maximum raw data rate of 54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s"
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