They found that over the first 24 hours, Omicron multiplied about 70 times faster inside respiratory-tract tissue than the Delta variant. When they ran the same experiments with the lung tissue, they found Omicron was actually worse at infecting those cells than either Delta or the original strain of the virus that originated in Wuhan. I've seen that study covered by a YouTube video that described the study conclusions a little differently. They described that Omicron multiplied 70 times faster inside respiratory-tract tissue than the Delta variant, as the article you posted indicated, but that the lung tissues were not infected as badly, which is consistent with the relatively milder symptoms being experienced with Omicron.
I think we have to take everything we see with a grain of skepticism.