I would have thought so too but what can I say 
It was discussed briefly in the above thread. Others pointed out that the 4k average might not include 0 balance accounts so won’t be exactly accurate but I would hazard a guess that more money has come in since the 3% announcement and we know user numbers are up the high 200’s now so not completely implausible.
Also, come to think of it, in another article recently there was a mention of freetrades transaction exceeding £1bn in September, which again I could see being a piece that might have warranted a bigger announcement too.
Edit. Here’s the article. It was discussed briefly at the same time as the launch for 3%. All if this is found in the “freetrade in the news” thread.
https://uk.reuters.com/article/uk-freetrade-rate-idUKKBN28B5IW
Now back on topic. Up to date user number anyone?