This may mean a lot, and this may mean nothing, depending on how you define a Bitcoin market share.
in this case these market shares are almost all defined by giant pumps solely on poloniex.
like so much related to market cap, it's a mirage. it is volume but that volume is happening largely in bitcoins. and these volumes are enabled by bitcoin's frictionlessness. i'd love to see fiat/alt volumes on coinmarketcap instead. it's speculation on top of speculation. all hot air.
there's probably significant fiat volume for certain coins but I wouldn't wait 3 days for a bank transfer so I could buy potcoin or something.