Ok, this was more complex than I thought. I hope I got it right and this gives you some pointers how I investigated. :)

Use type() to see what you are getting:

    >>> type(df.describe().mean())
    <class 'pandas.core.series.Series'>
    >>> type(df.describe().mean)
    <class 'method'>

Something without parenthesis cannot be a method call, at least not from a normal viewpoint. Instead you are trying to access the attribute "mean" of the result of describe() if you run df.groupby(df.var1).describe().mean. This attribute might very well be a method itself (a method object).

Last in that chain was describe(), so let's look at that: https://pandas.pydata.org/pandas-docs/stable/generated/panda...

It returns a "summary: Series/DataFrame of summary statistics", so calling .mean() on that, will call https://pandas.pydata.org/pandas-docs/stable/generated/panda...

Accessing .mean will instead return that method object itself.

By default pandas will return a string describing the data itself when printing a method:

    >>> df.describe()
           numeric   n2
    count      3.0  3.0
    mean       2.0  3.0
    std        1.0  1.0
    min        1.0  2.0
    25%        1.5  2.5
    50%        2.0  3.0
    75%        2.5  3.5
    max        3.0  4.0
    >>> df.describe().mean
    <bound method DataFrame.mean of        numeric   n2
    count      3.0  3.0
    mean       2.0  3.0
    std        1.0  1.0
    min        1.0  2.0
    25%        1.5  2.5
    50%        2.0  3.0
    75%        2.5  3.5
    max        3.0  4.0>
    >>> df.describe().mean()
    numeric    2.00
    n2         2.75
    dtype: float64

I assume this is what threw you off? You are not using the "results" of .mean in further code but were just looking at them, right?