Please read this in regards to bonus...

Please read this in regards to bonus shares.

https://www.investopedia.com/terms/b/bonusissue.asp

In short, they are paying for the bonus shares and give that to you, instead of giving you cash directly.
End effect is the tax treatment, and the ability for you to decide whether to realise it in cash or keep it for future growth.
i.e. you have the choice.

The % holding you have with the company should remain the same, but the value of the share should remain intact as well assuming no outside forces causing it to move. i.e that 1/200 share you get is indeed valued at the last close price, and share price shouldn't drop in theory (but in reality it probably will due to selling pressure).