MaxLag Mbean for Kafka Consumer

The Max lag Mbean is defined as "Number of messages the consumer lags
behind the producer". Now when I read the Mbean value it give me the count
as 0 (and occasionally some value like 130 or 340 )

ConsumerFetcherManager.test-consumer-group-MaxLag count = 0

But when I use the kafka.tools.ConsumerOffsetChecker I get following
as Lag value

*Group Topic Pid Offset
logSize *Lag* Owner*
test-consumer-group kafka-test 0 275985215
276195685 *210470* none

Are both the lags not related? Or is it like I am capturing the lag MaxLag
incorrectly?