Pandasql selecting loose matches from query

Question

I seem to be facing a weird bug or making a mistake somewhere in a simple SQL query. I'm using pandas and pandasql to bake an image to be run on AWS lambda.

Input CSV:

Org	Usage	Bucket
Abc	1GB	test-bucket-1
Def	2GB	test-bucket-10

CLI and Output:

import pandas as pd
from pandasql import sqldf
import boto3
df = pd.read_csv("testdata.csv", sep=",", header=0)
query = """select * from df where Bucket='test-bucket-1'"""
res=sqldf(query)
res.to_csv('pandas-op.csv')
print(res)

0,Abc,1GB,test-bucket-1 
1,Def,2GB,test-bucket-10

I only expect 0,Abc,1GB,test-bucket-1 to be shown. Why is it including partial match?