BTC market capitalisation is currently at ~45%
That's dominance not capitalization and the current rate is 47%.
Historically BTC market capitalisation has reached up to ~60% in bear markets
IIRC, it was 70% during the start of bitcoin's pump to its way to ATH.
What does this means for ALTS?
Most people are selling their alts for bitcoin, that's the meaning of it.
Relative to BTC altcoins will be loosing value, the market capitalisation of BTC has only increased 5%, imagine another 15%?
Please note that market capitalisation of BTC always increases in a bear market after drastic moves - it's now clear we are in a bearish trend and capitalisation has broken out (check trading view charts) so stay diligent.
And that only means that most investors are holding bitcoin and saving during the rainy days. This is the meaning of it and despite the market value has wiped more than half of it, this gives the idea that it's better to keep yours in btc right now.