Its a pre-ANN means that the website is still in beta phase, i think the 100 doge bonus was given so that players can test the casino and not to withdraw them. OP didn't really specify that but that's my best guess, unless you want to go as far as calling him a scammer which i think its bit of a overreaction.

Hello all players and users,

As you can see it is a pre-ann, the 100 doge coin is for testing the platform, it's stability and bugs reporting. We will officially launch the system on the 15th of August, then everyone who participates in the testing of this platform, will receive 100 doge coins directly in their wallet as  a Reward.

Till 15th of August, you will get reward in two ways;

1. As a participant you will get 100 doge coins after Testing of System

2. For reporting bugs on our discord channel, you get 10 doge coins, Our Discord Channel:
https://discord.com/invite/gCwt7eZWGd

N.B: Some of the doge coin withdrawal we processed was to check the functionality and stability. On 14th August, all balance will be null and participants will be credited 100 doge coins.