No, they are not lying but they are not claiming the same as you. They are not claiming 45,000 civilians have been killed they are claiming around that figure for people. Their data is also incorrect. Go to the appropriate topics and discuss/check there.
Also check for how many Hamas have been killed that are included in those numbers, 20,000.
Manipulated Data in Gaza Casualty Reporting Exposed by Think Tank
Discrepancies in Gaza Casualty Figures: An Analysis of Hamas Data By Associated Press
UN Cuts Death of Women and Children in Gaza by Half
Hamas admits one-third of its data on Gazan deaths is ‘incomplete’
Scrutiny Over Gaza Death Toll Figures: UK Statistics Watchdog Investigates Hamas's Data
How the Gaza Ministry of Health Fakes Casualty Numbers