From what I can see, there was no ill intention here. Floating rate can change at any point during the transaction, be it for price fluctuation or other reasons, both ETH (ARB) and LTC could have gone up or down to justify a 1$ drop from the original quote as this is 5% and LTC price changed over 10% in the past day. A sudden 2% drop on ETH and a 3% increase in LTC can cause a 5% (1$ on a 20$ transaction) value change.
The provider shows the amount paid out correctly (0.2266 LTC) and this may just be a visual bug on your end. The website also logged the amount paid as 0.2266 LTC.
If in the future you plan on using instant exchange services such as this one, know that floating rates are not certain. If you are looking for an exact number or value, use a fixed rate. It gives less $ but guarantees that amount in cryptocurrency unless the market crashes or changes drastically (downward)
Otherwise, this report is closed.