There are a few common reasons for differences in the reported usage.
1: New smart metres are not always accurate and can read higher or lower than expected. This has been especially observed for fast switching devices such as LED lights. Analogue metres have been found to be generally more accurate.
2: The Power Genius metering is generally faster (every cycle - 20milliseconds) than your utility company's meter (around 200-300milliseconds) so it picks up on fast energy changes throughout the day which may otherwise not be measured.
3: The start and finish times for the reporting period may be different. Power Genius resets the readings at midnight which may be different to the utility company's rating system.
4: The different metering systems handle power factor in different ways. Use Google search to compare 'Real Power', 'Apparent Power', 'Power Factor'.